Plasma Physics for the Radio Amateur V

We mentioned in Part One that most of what we know about the ionosphere is inferred from ground based radio, which is quite a distance from the ionosphere, generally speaking. We know what the ionosphere IS primarily from what it DOES. This is not always a very direct method.
At HIPAS Observatory, one of our sage elder scientists said, “Ionospheric research is like shooting a gun into a dark room and listening for whatever screams.”
I think that was a wonderfully apt description. Occasionally, we send a rocket through the ionosphere for “in situ” measurements, but these are very expensive and few and far between. There are some satellites that give us topside sounding, which allow us to see what the electron profile is ABOVE the critical height, something you can't do at ALL with ground based ionosondes.
And we also have plasma chambers. By “WE” we generally don't mean WE as individual hams, but WE as the scientific community as a whole. A lot of the phenomena we see in the natural ionosphere can be reliably reproduced in plasma chambers....things like long-delayed-echoes (an ion acoustic phenomenon), parametric amplifications, (no it's NOT your imagination, the ionosphere CAN amplify signals under the right conditions), and all kinds of weird and wonderful VLF phenomena like whistlers and choruses.
But despite all these tools, for the most part ionospheric studies are still pretty much shooting into a dark room and listening for the screams. The real trick is to have a finely trained ear. Or, preferably, a LOT of trained ears.
And this is where Amateur Radio fits in.
Doing ionospheric research from your back yard is not rocket science. But it does take good methodology and attention to detail...things most of us should have learned in high school chemistry class. However, I've learned, sadly enough, that anything resembling the scientific method seems to be lost on the majority of most new hams. This is most ironic, since ham radio is supposed to be a scientific hobby. All is not lost, however. Ham radio is still the best avenue for diving into low budget science. All it takes is some discipline. Here are the tools you need as a radio amateur to contribute to the state of the radio art, when it comes to ionospheric study.

1) Something resembling an actual S-meter. It's inexcusable in this day an age to have any receiver with a meaningless S-Meter. The technology is readily available to build an S meter that is absolutely consistent across the entire H.F. Spectrum, even if the sensitivity of the radio itself ISN'T. One of the primary principles of the scientific method is that you can't eliminate all instrumentation errors...but you CAN know exactly what they are and compensate for them! Get in the habit of giving REAL signal strength readings during all your H.F. Operating. In fact, if you start giving close estimates of actual FIELD STRENGTH, in microvolts per meter, it would be even better. It's not THAT difficult to calibrate the gain of your antenna, at least within a few dB of absolute. Any move in that direction is going to be a vast improvement of the normal way of doing business. NEVER promiscuously fling out S9 signal reports. Commit yourself to giving REAL signal reports!

2) Accurate record keeping. Start LOGGING meaningful signal strength readings from every station you work. And suggest that the other feller does the same. If you have a directional antenna, log the actual headings that give you the best signal. Do NOT assume these are great circle headings! This is CRUCIAL information to have if you want to make meaningful scientific contributions. Also, see if the beam heading you have for best reception ALSO is the best heading for your signal getting to the other guy! (Hint: it most likely will NOT!) The only way to know is to ask! LOG both these headings. Radio is only reciprocal in free space. The ionosphere does not qualify.

3) Count your skips. You need to know how many hops your signal is taking on its way to the other guy. And you need to know how many hops his signal is taking to get to YOU. Again, do NOT assume these are the same! You can usually get a good guess of this by looking at the critical height from a local ionosonde, and then do some simple trigonometry. You're basically going to be doing DF work in three dimensions. Here's a caution about skip counting, however. You can have overlapping skips! In other words, you can have both a one hop and a two-hop signal landing in the same place. Or a three hop and a five hop landing in the same place. Why? Because you don't launch a pencil beam on H.F.! You have a beam which can be as broad as a barn door....essentially with an INFINITE number of “takeoff” angles simultaneously. The only REAL way to resolve this is to have an antenna with a steerable vertical pattern...where you can sweep the elevation for maximum signal strength. If you can reasonably determine the vertical angle of arrival, you can resolve the skip count with some confidence. Again, this can't be done haphazardly, but it CAN be done. But you need to care.

4) You need to know your X from your O. This is CRUCIAL information to have, if you intend on doing meaningful ionospheric research. If you don't know whether you're dealing with an O ray or an X ray, you are basically one hand clapping in the dark. Remember, ALL ionospherically reflected signals will be either one or the other. Determining ray paths and processes is impossible without this information. Again, this property of H.F. Skywave is not a mere footnote; it's FUNDAMENTAL to how the ionosphere works.

5) You need to know your ERP That's Effective Radiated Power. You don't need to know this to six significant digits, but you do need to know it within a couple of dB. This means you need to know the gain of your antenna, at the frequency of interest, AND the actual R.F. Power reaching that antenna. The ancient and venerable method of measuring R.F. Current at the antenna is preferable, but if you know your transmission line losses with reasonable accuracy, you can come close enough by measuring your transmitter output power.

6) You need to care. This is THE most important ingredient of all. We radio amateurs need to justify our existence in order to maintain our highly coveted H.F. Frequencies. Frankly, this whole EMCOMM emphasis is really grasping at straws; it only addresses ONE out of five major points for Amateur Radio's existence as described in FCC Part 97.1. “When All Else Fails” may sound self-important, but what about the 99% of the time when all else WORKS? The fact is, we have a LOT more to offer when it comes to justifying ourselves when it comes to contributing to man's knowledge. Ionospheric research is in its infancy in terms of rigorous, methodical study. We can make a HUGE contribution here, with no more than the hardware on our desks and our gardens, and a bit of discipline. In fact we are the ONLY ones equipped to do this kind of research as a body. There IS no competition from the Department of Homeland Security, the Red Cross, your local fire department, or countless miscellaneous local whackers. If we, as radio amateurs, get back to doing what we're SUPPOSED to do, our future will be untouchable.

This series of articles has been a delight to read, and follow the on-line comments as well.

This last article has me thinking about participating in citizen science with our radio hobby. The way the hobby was explained to me, I thought surely that everything related to the propagation experience was well understood.

For my part I'll be thinking about my radio systems characteristics a lot harder than 'it works!'. I'll be looking for Eric's book.

Thanks for the nice feedback. After twiddling the ether for forty something years, the ionosphere is more fascinating than ever. There is a lot we DO know about it, but there's a lot we don't. But you have to be actually LOOKING for things. For example, most hams could (and do!) spend their entire lives successfully operating all over the world without knowing anything about X and O modes. A dipole, and most other antennas, for that matter, pick either of them up equally well. The reason the ionospheric scientists even started looking at circular polarization in the first place was because of the mathematics of refraction, and extrapolating from well-known optical phenomena. Again, scientists have known about X and O propagation for well over 70 years, it's only hams who seem to have missed the memo.

Parametric amplification is another one...but much less concrete and predictable than X and O mode propagation. For as long as hams have been hamming, there have been reports of signals that just "seemed" stronger than should have been possible. But nobody ever bothered to MEASURE them. (The need to stroke egos with inflated S reports never helped). However, the tiny handful of hams who DID bother to do meaningful measurements indeed verified that frequently long distance H.F. signals DO INDEED have less signal loss than free space path loss. This can only mean amplification of some sort.
Well, the process of parametrical amplification is well known, and as I mentioned above, easy to reproduce in a plasma chamber. What is NOT known is what sort of conditions "in the wild" need to occur to create parametric amplification. The only way to know is to be there when it happens...and to be prepared with some actual measuring tools when it happens. Again, most of this doesn't require National Bureau of Standards accuracy, but it does require at least a CLUE of one's antenna gain and such. This is something ANY ham can do.

My article, "Gimme an X, Gimme an O, What's that spell? RADIO!" is slated to be in QST in September. (Not chiseled in granite yet). If I get enough response from that, I'll definitely look into a book. I will also have some of this information in the Opus, but in a much more...ahem....wry form. :)

After being away from HR for many years I too am quite puzzled by all of the fuss over emcomm. Yes there is a role to play, but as you say, what do we do when all else works? I find it quite amusing when a ham picks up a cell phone to call another ham to help him/her get on the air for an emcomm drill. Or when a ham calls a friend in another state and tells him/her to get up on the local echo link so they can have a QSO. I am also finding there are many more operators than experimenters than there were back in the 60's and 70's and I'm sure before that.

You make some good points about getting more scientific about our operations and keeping accurate records. As a science teacher, this is difficult to teach my students to do. You give some very good suggestions about record keeping and using a reliable S meter/method of measurement.

So if we all become more disciplined and start keeping more accurate records, what do we do with it? Perhaps that is a topic for another article to come but it seems to me we need much more education on what data to collect, how to collect it, and then a depository for that data so those so inclinded can get at it and make sense of it.

Yea, I should have seen that with the big title letters. Leave it to me to not see the bigger picture.........so then, is there a part VI?...... or is this it.

Either way, this has been an interesting series of articles. With your writing style and the links you provided, I have a much better understanding of the subject than I would have from reading a text book.

I have often and still do, think of radio amateurs as sort of "amateur scientists" -- even the so-called appliance operators. "Something" made them go to the trouble of getting that ticket, and I always lean toward scientific curiosity.

These articles - if they did nothing else (but they do very well) - have reinforced that belief for me.

Er... we could do with some of that plasma fizzics for radio amateur No.5 over here. The bands are useless, there's more energy in a bucket of water than the ionosphere, so if you've got some spare in Alaska please send us a bit

I think 10 meter mobile is a fabulous mode. Far more reliable than 2 meters for local stuff, and you don't need repeaters. It's all but forgotten in most places.
Shame...if hams had kept it occupied during the low sunspots, the freebanders never would have showed up.

Although I've been a ham for over a quarter century, I have only recently developed an "above average" interest in the ionosphere. This interest has been sparked by my participation in Frequency Measurement Tests, where the effects of Doppler shift on ionospherically propagated radio signals can really skew one's results.

In an attempt to better understand how ionospheric turbulence was influencing my FMT results, I began looking at how Doppler shifts influenced my reception of standard frequency broadcasts from CHU and WWV. Plotting measured carrier frequency as a function of time over the period of several hours after sunset, an unmistakable (and almost predictable) cyclic pattern became evident in my measured data:

The latter two plots involve plotting data for both vertically and horizontally polarized receiving antennas. Note that the measured frequency often changes when antenna polarization changes.

I have also looked into the abrupt phase changes that sometimes occur when a received signal undergoes a rapid and deep fade. Realizing that a change in polarization could explain both the observed fade and the corresponding phase shift, I constructed a fully-balanced ferrite loopstick antenna for CHU reception (3.330 MHz) that could be easily and quickly maneuvered in all 3 dimensions. I discovered that I could often recover a carrier undergoing a deep fade by simply rotating the loopstick 90 degrees in azimuth. At first, I thought this implied a drastic change in the direction of arrival was taking place. Then I remembered that at 3 MHz and a 365 mile distance to CHU, the signal was mostly likely arriving from a very high angle of elevation. Therefore, rotating the azimuth of the loopstick was simply "twisting" its polarization sensitivity (coupling coefficient) to the high angle wave.

One of my pet projects at Hipas Observatory was a doppler ionosonde. The whole purpose of this was to measure how FAST the ionosphere moves under the influence of artificial heating. A side benefit of this was that we could also detect the Natural movement of the ionosphere as well. Right after sundown, when the ionsphere recedes, we typically saw it moving at over 700 meters/second! It would continue doing this for 15 or 20 minutes until it reached its final nighttime "resting" place!

While it is true that signal-to-noise ratio is indeed the important factor for communications, when it comes to ionospheric studies, it's just about meaningless. It's REAL signal strength that matters. This is how you determine the physical processes involved, as well as the path, polarization, electron density, total electron content, and any number of factors.

I am reminded of an old receiver, the SP-600 which had an S meter with two scales. One was our old friend S1-S-9 + db over. The other was mV at the antenna terminal (supposedly). What I'm wondering is if you divided the meters of your antenna by the mV if you could get mV/m on such an "S" meter ?

73, TR
K6GC,the Great Circle Station
in the state of Jefferson !
http://www.ijpr.org/Page.asp?NavID=1033

K6GC,
The Hammarlund probably had a scale en uV (microvolts) not mV (milivolts).

If that scale was effectively in uV/m (microvolts per meter) then it was field strength and not uV at the antenna terminals.

Field strength is based on the impedance of free space that's 120 * pi ohms, or ~377 ohms, which represents the relative intensity of the H field to the E field in the propagating wave. So "meters" here refers to the field strength of the wave front as intercepted by the antenna, not the length of the antenna itself.
(From the power density in W/m2 (watts per square meter) the field strength can be derived in V/m assuming the free space impedance is known.)

If it was uV at the antenna terminals, then it's easy because the only thing needed is to know the input impedance of the receiver. In the SP-200 the antenna input is a shielded air core transformer, so the input impedance is probably constant for much of the frequency range of the receiver.

These days the most common unit is the dBm (deciBels refered to 1 milliwatt over 600 ohms, or over 50 ohms of input impedance) for signal strength and it would be very nice to have this in our transceivers with/instead of the S9 scale.
Even my cheap blackberry cellphone shows the signal strength in dBm!

"It's inexcusable in this day an age to have any receiver with a meaningless S-Meter"

Except that most of the available amateur transceivers on the market don't have accurate S-Meters. With processors in the transceiver it would certainly be possible to calibrate the S-Meter accurately but it would require a calibration process on each individual receiver and any change in overall gain with component aging would require recalibration.

There seems to be an extraordinary amount of energy expended on this topic. Is there any way at all to transfer some of it to the ionosphere itself? How about a 10 mile diameter foil satellite at virtual height of the F2 layer?
In 50 years of radio I cannot recall an ionospheric doldrums that equalled the depth of this one. Are we at the start of another "Maunder Minimum"? If so, will we then have another "Little Ice Age"?

it's been pretty good. We did have a major coronal mass ejection last week, but that's calmed down. We may not get the heights of 1957, but the critical frequency is hitting the 6 MHZ level, which is still fine for anything below 20 meters at low angles.